Organic semiconductors, including pentacene derivatives and polythiophenes, are useful as charge-transporting materials in thin film transistors (TFTs), diodes, photovoltaic devices, and the like. The semiconductors, which are soluble in organic solvents, may be fabricated for use in these electronic devices by liquid deposition processes. Their ability to be fabricated via common liquid deposition processes allows for simple and cost effective manufacturing as compared to costly conventional photolithographic processes utilized in the production of silicon-based devices, such as hydrogenated amorphous silicon TFTs.
Moreover, organic semiconductors have excellent durability and flexibility characteristics, permitting the fabrication of flexible semiconductor components on flexible plastic substrates, thereby enabling creation of mechanically durable and structurally flexible electronic devices. These soluble organic semiconductors are particularly valuable in the manufacture of large image sensors, flat-panel displays, electronic paper and other large-area electronic devices. These organic semiconductors may also find application in low-cost microelectronics such as smart cards, radio frequency identification (RFID) tags, and memory/storage devices where the high costs of packaging silicon circuits may become limiting.
However, most organic semiconductors are prone to interaction with atmospheric oxygen, particularly when exposed to light. For example, p-type semiconductors such as pentacene readily react with atmospheric oxygen in the presence of UV and visible light, leading to severe degradation of its semiconductor properties. Similarly, oxygen is also an excellent electron trap for n-type organic semiconductors, and may prevent them from functioning properly as electron transporting media. Accordingly, when working with many organic semiconductor materials, rigorous precautions have to be undertaken during processing and device fabrication to exclude environmental oxygen and/or light to avoid or minimize these degradative effects. These precautionary measures add to the cost of manufacturing, offsetting the appeal of organic semiconductor devices as a low-cost alternative to amorphous silicon devices, particularly for large-area device applications.
The following documents provide background information:
A. R. Brown et al., “Logic Gates Made From Polymer Transistors and Their Use in Ring Oscillators,” Science, Vol. 270, pp. 972-974 (1995).
A. R. Brown et al., “Precursor Route Pentacene Metal-Insulator-Semiconductor Field-Effect Transistors,” J. Appl. Phys., Vol. 79, No. 4, pp. 2136-2138 (1996).
K. P. Weidkamp et al., “A Photopatternable Pentacene Precursor for Use in Organic Thin-Film Transistors,” J. Am. Chem. Soc., Vol. 126, pp. 12740-12741 (Published on Web Sep. 16, 2004).
Beng S. Ong et al., “High-Performance Semiconducting Polythiophenes for Organic Thin-Film Transistors,” J. Am. Chem. Soc., Vol. 126, No. 11, pp. 3378-3379 (published on web Mar. 2, 2004).
The conventional approaches for improving the stability of organic semiconductors often lead to compromises on other desirable characteristics of the semiconductors including for instance transistor mobility, processability, reproducibility, and the like.
Therefore, there is a need, which is addressed by embodiments of the present invention, for simple and reproducible methods to stabilize organic semiconductor materials during processing to avoid or minimize performance degradation when fabricating electronic devices under ambient conditions.